Optoelectronic devices and systems are widely used in today's telecommunications and other industries. In optoelectronic systems, an electrical signal is converted to an optical signal that travels along an optical transmission medium such as an optical fiber, and is then typically converted back to an electrical signal. A high optical coupling efficiency between the optical transmission medium that carries the optical signal, and the device that converts the optical signal to an electrical signal (or vice versa), is required for good optoelectronic connections and system functionality. The precise placement and accurate alignment of the optical fiber, with respect to other optoelectronic components, is required for a high optical coupling efficiency. The electrical-to-optical and optical-to-electrical optoelectronic connections are typically made in optical subassemblies (OSAs) such as TOSAs (transmission OSAs) and ROSAs (receiving OSAs) or other optical packages. Optical fibers are typically held in place within such an OSA or optical package, by being joined to a fixed member such as a substrate, using an epoxy.
Non-hermetic optoelectronic packages include the shortcoming that epoxy fiber bonding is relatively weak due to moisture absorption by the epoxy. This absorption of moisture from the environment causes saturation and deformation of the cured epoxy and causes the position of the optical fiber to shift as the optical fiber becomes displaced or detached. With the accuracy of the optical fiber placement so critical in maintaining high optical coupling efficiency, a shift in the position of the optical fiber results in partial or full misalignment between the optical fiber and the device to which it is desirably coupled. This results in poor optical coupling and/or device failure.
Known approaches for addressing this problem in non-hermetic packaging include the use of an epoxy which has lower moisture absorption characteristics and stronger bonding capabilities in moisture, and the use of solder in place of epoxy. Each of these approaches includes shortcomings. Epoxies with low moisture absorption and stronger bonding capabilities may increase package life, but only for a limited time because all epoxies are somewhat porous and absorb moisture to some degree. Eventually, the absorbed moisture diffuses throughout the epoxies which become saturated and fail. For example, conventional packages made using such epoxies cannot survive 85/85 damp heat testing for over 800 hours. The second approach of soldering an optical fiber to a substrate is limited by the spacing within the package. Furthermore, the procedure used to solder the optical fiber may render many packages unsuitable for fiber soldering. Moreover, even in packages where fiber soldering is an option, the fiber soldering causes flux cleaning and thermal strain and stress issues which are potential factors for package failure.
It would therefore be desirable to provide a scheme for bonding optical fibers to a fixed member, such as a substrate, in a non-hermetic package such that the optical fiber remains precisely and accurately aligned. The present invention addresses these needs.